1. Field of the Invention
The present invention relates to an electrical equipment such as a television receiver or video tape recorder, and more particularly to a cumulative time measuring method and apparatus for measuring a total operation time of the equipment and storing it.
2. Description of the Prior Art
Japanese Provisional Publication No. 1-136291 discloses a time monitoring system whose time measurement starts at each turning-on of a main electric source of an electrical equipment and cumulatively updates cumulative time data stored in a nonvolatile memory at proper time intervals on the basis of a time period measured by a digital signal processing system such as a microprocessor or one-chip microcomputer. The cumulative time data recorded in the nonvolatile memory corresponds to a total operation time of the equipment and is available for a maintenance of the equipment. In general, a cumulative time measuring method is arranged such that the cumulative time data is cumulated in the nonvolatile memory by each predetermined time period such as 10 minutes. That is, when the elapsed time from the turning-on of the measuring command becomes integer times 10 minutes, the cumulative time data is increased by 10 minutes.
However, such a conventional method where the cumulative time data is cumulated by 10 minutes unit as mentioned above, has a problem that the accumulated error of the cumulative time data becomes very large wherein a concrete numeral such as 10 minutes is not a nature of the problem, and is merely used for facilitating the understanding of the explanation. That is, when 10 minutes has elapsed after the turning-on of the measuring command, 10 minutes is added to the cumulative time data, and when 10 minutes has further elapsed, 10 minutes is again added to the cumulative time data. Accordingly, in case that a time period during which the measuring command is turned on is in a range from 10 minutes within 20 minutes, the increment amount of the cumulative time data is 10 minutes in every cases. Therefore, as to an increment amount for one time due to the change of the measurement command from ON to OFF, there is an error of 9 minutes 59 seconds in maximum, and 5 minutes in average. Since this error is accumulated by each turning-on of the measurement command, if the number of times of the turning-on becomes several thousands or further several ten thousands, the accumulated error becomes extremely large.